The invention relates in general to magnetic field sensors and more particularly to integrated magnetic field sensors formed on a single semiconductor die and requiring the use of a magnetic field for functions such as domain setting, calibration, establishing a bias or offset magnetic field, providing a feedback field, determining a sensor transfer characteristic, or other functions requiring a magnetic field.
The invention has application to a variety of magnetic sensors or transducers. These include, but are not limited to magnetoresistive transducers, giant and colossal magnetoresistive transducers, magnetodiodes, magnetotransistors and Hall effect transducers.
Magnetic field sensing devices may be used in many applications, including, but not limited to, solid state compassing, e.g., in automobiles; in signature detection, e.g., metal detection; and in anomaly detection, e.g., position sensing.
Solid state compassing may be used in personal items, for example, in a watch. Position sensing may be used to sense the position of a medical device, such as a catheter within the body of a patient. These and other applications have created requirements for magnetic sensing devices that are of a smaller size and that require less power than the devices of the past.
Extremely small magnetic field sensing devices can be made utilizing long thin strips of a magnetoresistive film of an NiFe material, such as Permalloy.TM.. The magnetization of the film generally forms an angle with the current, and the resistance of the film depends on this angle. When the magnetization of the film is parallel to the current, the resistance is at a maximum, and when it is perpendicular to the current, the resistance has its minimum value. The magnetization in these films must be set in a single domain state before it is ready to sense magnetic fields. Although there may be situations where a magnetoresistive transducer can sense magnetic fields even if it is in a multiple domain state, for purposes of repeatability, it is essential that the magnetization of a magnetoresistive transducer magnetic sensing element be in a single domain state. The set-reset function is described in U.S. Pat. No. 5,247,278.
Magnetic field sensing devices may be constructed of elongated magnetoresistive strips which make up the four separate elements, or legs, of a wheatstone bridge. The legs are then oriented to be sensitive to a field perpendicular to the strips, which results in all strips being parallel in the bridge configuration. Bridge configurations which will conserve space include arranging the four elements in a single plane into a single column or row sometimes referred to as 1.times.4 configuration, or arranging the four elements into two side-by-side sets of two elements each; sometimes referred to as a 2.times.2 configuration. An illustration of a 1.times.4 configuration with set-reset conductor 12 and elements 13 is shown in FIG. 6a. An illustration of a 2.times.2 configuration with set-reset conductor 14 and elements 15 is shown in FIG. 6b. Both configurations are discussed in U.S. Pat. No. 5,247,278.
The testing, setup, compensation, or calibration of magnetic field sensing devices represents an important area. A second important area is the use of the sensing devices in a feedback control application. The function needed in both areas is the ability to produce a known magnetic field at the magnetic field sensor. This known field and the ability to vary the field allows one to measure the response of the magnetic field sensor and perform set up, sensitivity and calibration operations, and to use the sensor in feedback applications.
Thus a need exists for a simple self contained device that is very small, and requires very little power, to provide a magnetic field for setting and resetting the magnetic domains in a sensor and for producing a known magnetic field for testing, set up, and calibration, as well as for feedback applications of a magnetic field sensor.